Shapes of chondrules determined from the petrofabric of the CR2 chondrite NWA 801          下载免费PDF全文

Christopher R. J. Charles  Pierre-Yves F. Robin  Donald W. Davis  Phil J. A. McCausland 《Meteoritics & planetary science》2018,53(5):935-951

The approximately spherical shapes of chondrules has long been attributed to surface tension acting on ~1 mm melt droplets that formed and cooled in the microgravity field of the solar nebula. However, chondrule shapes commonly depart significantly from spherical. In this study, 109 chondrules in a sample of CR2 chondrite NWA 801 were imaged by X-ray computed tomography and best-fitted to ellipsoids. The analysis confirms that many chondrules are indeed not spherical, and also that the chondrules’ collective shape fabric records a definite 13% compaction in the host meteorite. Dehydration of phyllosilicates within chondrules may account for that strain. However, retro-deforming all chondrules shows that a large majority were already far from spherical prior to accretion. Possible models for these initial shapes include prior deformation of individual chondrules in earlier hosts, and, as suggested by previous authors, rotation of chondrules as they were solidifying, and/or “streaming” of molten chondrules by their differential velocities with their gaseous hosts after melting. More in situ 3-D work such as this study on a variety of unequilibrated chondrites, combined with detailed structural petrography, should help further constrain these models and refine our understanding of chondrite formation.  相似文献   

Instability structures, synsedimentary faults and turbidites, witnesses of a Liassic seismotectonic activity in the Dauphiné Zone (French Alps): A case example in the Lower Pliensbachian at Saint-Michel-en-Beaumont     

Franoise Bergerat  Pierre-Yves Collin  Anne-Cline Ganzhorn  Franois Baudin  Bruno Galbrun  Isabelle Rouget  Johann Schnyder 《Journal of Geodynamics》2011,51(5):344-357

Instability structures, synsedimentary faults and turbidites have been studied in the Lower Pliensbachian succession of Saint-Michel-en-Beaumont, belonging to the Taillefer block, an ancient half-graben emplaced during the Liassic Tethyan rifting. Geometrical and mechanical analyses demonstrate that the instability structures occurred thanks to movements along spineless synsedimentary normal faults, when the turbiditic and limestone layers were already case-hardened and partly fractured by tension gashes even when the mudstones were still unlithified. Both the tension gashes and the synsedimentary faults are homogeneous in strike with the major regional faults and are in good agreement with the regional direction of extension for this period. The characters of the turbiditic beds, with erosive base, graded bedding, and incomplete Bouma sequence, are in favour of a seismic origin. Instability structures, spineless synsedimentary faults and turbiditic inflows are thus considered as seismites and interpreted as the result of high seismicity periods including some events with M > 5 in the general extensive ambiance of the Liassic Tethyan rifting. The analysis of the geometrical relationships between all these sedimentary features allows to distinguish the successive stage of occurrence of an instability structure, from the sedimentation of alternating marls and limestones, and sudden turbiditic inflows, then early case-hardening of the turbidites, until the important seismotectonic event generating the spineless normal faults, themselves triggering the fall of indurated blocks and locally the forming of breccias. The Ornon Fault, which constitutes the border of the Taillefer block, 15 km eastward, played a major role during the Liassic sedimentation and may represent the major seismic fault related to the seismites occurrence in the Beaumont basin.  相似文献   

Comprehensive study of the drying behavior of Boom clay: Experimental investigation and numerical modeling          下载免费PDF全文

Julien Hubert  Erwan Plougonven  Noémie Prime  Angélique Léonard  Frédéric Collin 《国际地质力学数值与分析法杂志》2018,42(2):211-230

This paper presents a thermo‐hydro‐mechanical framework to model the drying behavior of Boom clay. First, the experimental campaign conducted Noémie Prime is briefly presented because it is used to validate the model. The data acquisition and processing is emphasized because of the use of X‐ray microtomography to be able to more accurately compare experimental and numerical strain fields. The different submodels are introduced. Numerical simulations are performed to illustrate the capability of the proposed model to reproduce the observed behavior. Finally, a comprehensive sensitivity study on several key model parameters associated with the water retention curve, and the permeability of the medium, is performed to get a better understanding of the physics behind the coupled model.  相似文献   

Orbital calibration of the Early Kimmeridgian (southeastern France): implications for geochronology and sequence stratigraphy     

S. Boulila  B. Galbrun  L. A. Hinnov  P.‐Y. Collin 《地学学报》2008,20(6):455-462

Classic stratigraphic methods rarely provide high‐resolution correlations between intrabasinal sedimentary sequences, which are important to understand the origin of sedimentation process and its environmental change. In this study, we investigate high‐resolution cyclostratigraphic correlation from magnetic susceptibility in two Early Kimmeridgian pelagic marl‐limestone successions, at La Méouge and Châteauneuf‐d'Oze, southeastern France. Spectral analysis reveals the complete suite of orbital frequencies (precession, obliquity, and eccentricity) with the marl‐limestone couplets being primarily precession‐driven. Frequencies detected by the spectral analysis are similar between the sections, but their relative amplitudes are somewhat different, linked to the palaeoenvironmental position and the completeness of the sections. High‐resolution correlation reveals two significant hiatuses at Châteauneuf‐d’Oze. Early Kimmeridgian Platynota, Hypselocyclum, and Divisum ammonite zones were orbitally calibrated for an ultra‐high resolution assessment of geological time. Finally, strong 405‐kyr eccentricity cycles are recorded as third‐order depositional sequences.  相似文献   

Long term evolution of distant retrograde orbits in the Earth-Moon system   总被引：1，自引：0，他引：1  

Collin?BezroukEmail authorView author&#;s OrcID profile  Jeffrey?S.?Parker 《Astrophysics and Space Science》2017,362(9):176

This work studies the evolution of several Distant Retrograde Orbits (DROs) of varying size in the Earth-Moon system over durations up to tens of millennia. This analysis is relevant for missions requiring a completely hands off, long duration quarantine orbit, such as a Mars Sample Return mission or the Asteroid Redirect Mission. Four DROs are selected from four stable size regions and are propagated for up to 30,000 years with an integrator that uses extended precision arithmetic techniques and a high fidelity dynamical model. The evolution of the orbit’s size, shape, orientation, period, out-of-plane amplitude, and Jacobi constant are tracked. It has been found that small DROs, with minor axis amplitudes of approximately 45,000 km or less decay in size and period largely due to the Moon’s solid tides. Larger DROs (62,000 km and up) are more influenced by the gravity of bodies external to the Earth-Moon system, and remain bound to the Moon for significantly less time.  相似文献   

H/V ratio: a tool for site effects evaluation. Results from 1-D noise simulations   总被引：9，自引：1，他引：9  

Sylvette Bonnefoy-Claudet  Cécile Cornou  Pierre-Yves Bard  Fabrice Cotton  Peter Moczo  Jozef Kristek  Donat Fäh 《Geophysical Journal International》2006,167(2):827-837

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Isotope characterization of lead in galena from ore deposits of the Aysén Region, southern Chile     

Brian K. Townley  Collin I. Godwin 《Mineralium Deposita》2001,36(1):45-57

Lead isotope analyses of galena from five ore deposits and six prospects in the Aysén region of southern Chile are reported. Most of the deposits are either low sulfidation epithermal gold–silver veins or skarn and manto deposits; the majority are either suspected to be, or dated as, Late Jurassic to mid-Cretaceous. Galena lead isotope data for most of the deposits from southern Chile cluster near the “orogene” within a “plumbotectonic” model framework. Average values (²⁰⁶Pb/²⁰⁴Pb=18.53, ²⁰⁷Pb/²⁰⁴Pb=15.63, and ²⁰⁸Pb/²⁰⁴Pb=38.50) are near Jurassic to Cretaceous model ages on the “orogene” curve of Zartman and Doe (1981) and the second-stage curve of Stacey and Kramers (1975) on a ²⁰⁶Pb/²⁰⁴Pb versus ²⁰⁷Pb/²⁰⁴Pb plot. These model ages are compatible with absolute ages as currently known. The elongate trends in the general cluster indicate mainly an orogenic model fit, suggesting variable mixing of lead from different sources, mainly model upper crust and lesser model mantle and lower crust reservoirs. Galena lead associated with one deposit (El Faldeo) is relatively radiogenic, and lies near a Jurassic age on the “upper crustal” curve of Zartman and Doe (1981), which is compatible with the Ar/Ar age of the deposit. Galena lead isotope clusters define three main groups of deposits. These three groups appear to be related to three mineralizing events, dated by K–Ar and Ar/Ar, in the Late Jurassic (group 3), and in the Early and mid-Cretaceous (groups 1 and 2 respectively). Averages for group 1, the northern group including El Toqui and Katerfeld, are ²⁰⁶Pb/²⁰⁴Pb=18.51, ²⁰⁷Pb/²⁰⁴Pb=15.62, ²⁰⁸Pb/²⁰⁴Pb=38.48. Averages for group 2, the southern group with Fachinal and Mina Silva, are ²⁰⁶Pb/²⁰⁴Pb = 18.56, ²⁰⁷Pb/²⁰⁴Pb=15.63, ²⁰⁸Pb/²⁰⁴Pb=38.52. Averages for group 3, the southernmost group with the El Faldeo, Lago Chacabuco and Lago Cochrane prospects, are ²⁰⁶Pb/²⁰⁴Pb=18.83, ²⁰⁷Pb/²⁰⁴Pb=15.65, ²⁰⁸Pb/²⁰⁴Pb=38.63. The Cretaceous deposits (groups 1 and 2) contain orogene-type lead that becomes increasingly radiogenic southward. Lead from the Late Jurassic deposits (group 3) appears to reflect mixing of orogene lead with highly radiogenic lead. The observed linear array of lead in group 3 probably reflects mixing of orogene lead with highly radiogenic lead, which was likely extracted by selective leaching of mineralizing hydrothermal solutions from the metamorphic basement. Received: 10 July 1999 / Accepted: 15 July 2000  相似文献   

Magnotospheric imaging of high latitude ion outflows     

D. E. Garrido  R. M. Robinson  Y. T. Chiu  H. L. Collin  R. W. Smith  D. W. Swift 《Annales Geophysicae》1994,12(2-3):169-182

High latitude ion outflows mostly consist of upward streaming O⁺ and He⁺ emanating from the ionosphere. At heights above 1000 km, these flows consist of cold and hot components which resonantly scatter solar extreme ultraviolet (EUV) light, however, the ion populations respond differently to Doppler shifting resulting from the large relative velocities between the ions and the Sun. The possibility of optical detection of the Doppler effect on the scattering rate will be discussed for the O⁺ (83.4 nm) ions. We have contrasted the EUV solar resonance images of these outflows by simulations of the 30.4 nm He⁺ and 83.4 nm O⁺ emissions for both quiet and disturbed geomagnetic conditions. Input data for the 1000 km level has been obtained from the EICS instrument aboard the Dynamics Explorer satellite. Our results show emission rates of 50 and 56 milli-Rayleighs at 30.4 nm for quiet and disturbed conditions and 65 and 75 milli-Rayleighs at 83.4 nm for quiet and disturbed conditions, respectively, obtained for a polar orbiting satellite and viewing radially outward. We also find that an imager at an equatorial distance of 9 R_E or more is in a favorable position for detecting ion outflows, particularly when the plasmapause is depressed in latitude. However, an occultation disk is necessary to obscure the bright plasmaspheric emissions.  相似文献   

TWO REFERENCE MATERIALS, TRACHYTES MDO-G AND ISH-G, FOR ARGON DATING (K-AR AND ⁴⁰AR/³⁹AR) OF PLEISTOCENE AND HOLOCENE ROCKS     

Pierre-Yves GILLOT  Yves CORNETTE  Nathalie MAX  Bruno FLORIS 《Geostandards and Geoanalytical Research》1992,16(1):55-60

With the recent extension of K-Ar dating methods within the Upper Pleistocene time, the use of new standards is recommended to allow calibration and inter-laboratory comparisons. For this purpose, two pure microlitic groundmass reference materials were prepared from trachy-basaltic lavas: Trachyte (MDO-G) from Mont Dore, Puy de Sancy, Massif Central is around 250 000 years old; the second Trachyte (ISH-G) from the Isle of Ischia, Gulf of Naples (Italy), is historical: Arso flow erupted on Christmas 1301 - January 1302 AD.  相似文献   

Damage seismic scenarios for Angra do Heroísmo, Azores (Portugal)     

Idalina Veludo  Paula Teves-Costa  Pierre-Yves Bard 《Bulletin of Earthquake Engineering》2013,11(2):423-453

Angra do Heroísmo, located in Terceira Island, is the main town of the Central Group of Azores Archipelago and it is classified as World Heritage by Unesco. The preservation of this patrimony, located inside a seismic region, includes the implementation of a policy to protect it against earthquakes. The development of credible damage scenarios could help this objective, as they can be used in prevention measures to minimize the impact of future earthquakes. Two methods were used for seismic damage estimation: the capacity spectrum method and a new method, based on the direct response of a 1D non-linear oscillator to simulate the building seismic performance. Both methods seem to overestimate the damages for the near sources, but this could be due to the empirical model used to estimate the input ground motion. Comparison with the damage observed after the January 1st, 1980 earthquake show a large discrepancy with an underestimation bias, which can be explained, mainly, by the difference of building performance and on the plausible hypothesis of 2D site effects.  相似文献